Excessive alcohol intake is a leading cause of non-ischemic dilated cardiomyopathy. While the pathogenesis of alcoholic cardiomyopathy is poorly understood, a direct toxic role for alcohol and its principal metabolite acetaldehyde has been postulated. Until recently, the heart has been viewed as an organ formed from terminally differentiated cells. Data have emerged however to support the existence of cardiac- and extra-cardiac-derived stem cells capable of replacing dead myocardial cells. This proposal seeks to test the hypothesis that one central mechanism by which alcohol damages the heart is by impairing the ability of endogenous stem cells to replace damaged heart tissue. We propose to use cellular and whole animal approaches to test this hypothesis and to explore the potential use of cellular therapies for treatment of the alcohol-damaged heart. To begin our study we will seek to quantify cardiomyocyte stem cell replacement during alcohol exposure, as well the contribution of replacement cells derived from the bone marrow. Preliminary data presented in this application demonstrates that alcohol can directly affect skeletal satellite cell differentiation. We will extend these studies by exploring the effect of alcohol on progenitor cells isolated from the heart as well as the cardiomyocyte-specific differentiation of embryonic stem cells. Tissue-specific stem cell differentiation requires the coordinated input of lineage-determining transcription factors. As shown in our preliminary data, alcohol alone and in conjunction with the metabolic enzyme alcohol dehydrogenase (ADH), significantly reduces the transcriptional activity of the cardiac determination transcription factor GATA4. To better understand how alcohol may directly affect cardiac-specific stem cell differentiation we will study how alcohol affects GATA4-dependent transcription. Finally to better understand the impact of alcohol metabolism and acetaldehyde on cardiac stem cells we will study a transgenic line of mice that express alcohol dehydrogenase in the heart. By exposing heart progenitor cells to alcohol, with and without ADH overexpression, we will seek to better understand the effect of ethanol and its principal metabolite on progenitor cell proliferation and differentiation. To complete our analysis we will seek to correlate the contractile abnormalities of alcoholic myopathy with stem cell number, and then determine the role of exogenous stem cell replacement in the treatment of experimental alcoholic cardiomyopathy. Alcoholic cardiomyopathy remains a significant public health problem. Studies outlined in this application are designed to provide needed insight into the role of alcohol on stem cell-based tissue-repair.